Mi. Carvalho et al., MODULATIONAL INSTABILITY OF QUASI-PLANE-WAVE OPTICAL BEAMS BIASED IN PHOTOREFRACTIVE CRYSTALS, Optics communications, 126(1-3), 1996, pp. 167-174
The modulational instability of quasi-plane-wave optical beams in bias
ed photorefractive media is investigated under steady-state conditions
. The spatial. growth rate of the sideband perturbations is obtained b
y globally treating the space-charge field. Our analysis indicates tha
t the growth rates depend on the strength of the externally applied el
ectric field and, moreover, on the ratio of the optical beam's intensi
ty to that of the dark irradiance. Our results are then compared to pr
evious local treatments of the space-charge field equation. The two ap
proaches are found to be in good agreement in the low spatial-frequenc
y regime provided that the external bias field is sufficiently high. C
onversely, in the high spatial-frequency region notable differences ma
y exist. Relevant examples are provided.